In such applications leakage problems arise from time to time and particularly in the conveyance of gases at high pressure. In the main this is not primarily due to faulty design of the sealing rings but to the difficulty of ensuring that machining of the joint components is of a sufficiently high standard regardless of where they have been manufactured.
The leakage problem is particularly acute when the flanges are intended to be drawn into face to face abutment instead of slight spacing or stand-off. There are many situations where it is essential to have face to face assemblies.